Texturing yarn

ABSTRACT

A method of controlling the manufacture of false twist textured yarn characterised by adjusting non-isothermally in a closed loop the heat flux taken up by the yarn in tension to a specific yarn dyeability. Adjustment can be achieved by feeding back the output of a direct-acting yarn texture sensor to control at least one of yarn heater heat supply, yarn twist speed and yarn feed speed. The sensor is arranged to sense at least one of textured yarn speed, yarn temperature, yarn bulk and yarn tension. A very compact texturing line is possible when the control method is applied.

BACKGROUND OF THE INVENTION

This invention relates to the manufacture of yarn by the false twisttexturing method in which a multistrand synthetic yarn is given a falsetwist and heated to "texture" or "bulk" the yarn. Among other advantages"texturing" improves the feel of garments made from the yarn.

Typically a very large machine is needed for texturing yarn. Thismachine includes numerous similar portions, sometimes as many as 216, ineach of which yarn is textured. The portions are known as "positions"and each position has a supply of yarn to be textured, a texturingapparatus and a take-up for the textured yarn. Each texturing apparatusis some six metres high with heating and cooling zones some two to threemetres long and subject to varying ambient conditions. All the positionsare intended to operate at the same texturing conditions and all aresupplied with the same type of yarn. In theory the whole machine willoperate at the same conditions and each position will produce yarn whichis textured in the same way. However, in such a large machine theconditions will not always be the same from position to position andvariations in texturing are inevitable despite careful design andconstant attention to operation. In particular the heating arrangementis inflexible and it is appropriate to classify such machines asisothermal, also recognising the aim of an identical heat state at eachposition. Despite the above developments the need for more economicmanufacture demands improvements above the speed and quality nowachieved. In particular the dyeability of the yarn can vary due toinconsistency of yarn texturing input and this can lead to the rejectionand waste of much material.

In EP-A-20143974 (Teijin Ltd) there are suggestions for an isothermalmethod of producing textured polyester yarn in which the heater lengthcan be reduced to less than 1.8 metres. Specifically a heater length of0.65 to 0.70 metres with a yarn speed of 400 metres per minute and astraight line path is proposed. However the method requires a specialheater called a "non-touch" type with a bow shaped yarn path in whichthe yarn is guided by plates with shaped slits to suppress a yarnballoon. The heater temperature is from 300° C. to 800° C. If the yarnbreaks in the heater it will be destroyed by the very high temperatureof the heater burning off the yarn. The very high temperature is neededas heat is transferred to the yarn by radiation in an open environmentso heat loss is high. Because the yarn must not touch the heater theyarn must be "lifted off" during start-up and similar interruptions tocontinuous running.

In U.S. Pat. No. 4888945 (Murata), and equivalent DE-A-3811437, aquality control technique for a conventional yarn texturing apparatus isdescribed which avoids harm to yarn quality which can be caused bytesting yarn during production. The technique is based on measurementsmade while yarn is being wound onto the empty bobbins when first loadedto replace bobbins doffed with full packages.

EP-A-20271252 (Rieter Scragg) describes a conventional isothermal yarntexturing apparatus to which a monitoring method is applied. Thismonitoring method involves measuring the difference in crimped yarnvelocity when under high tension (velocity V1) and low tension (velocityV2). The quantity V1-V2×100 is defined as the crimp velocity and isstated to V1 have a positive relationship to the crimp retractionquantity.

GB-A-841255 (Dunlop) describes an apparatus for determining the changein length under load of a length of filamentary material travelling fromone point to another. Lengths of material under zero and known tensionare compared in percentage terms to give extensibility of the material.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved yarntexturing production technique.

According to the invention there is provided a method of controlling themanufacture of false twist textured yarn characterised by adjustingnon-isothermally in a closed loop the heat flux taken up by the yarn intension to a specific dyeability.

In particular the method permits compensation for the effects of yarntension and shrinkage variation in a supply package on texturing.

The method permits variation of texturing conditions in a singleposition. The method permits in a multiple position machine variationfrom one position to another so that different texturing conditionsexist in individual positions at the same time. In this way, ifrequired, the specific dyeability can be achieved from all the positionsat the same time by providing appropriately different conditions.

The adjustment in a closed loop may be under a control signal generatedby one of a yarn tension sensor, a yarn temperature sensor, a yarndriven drum sensor.

A relaxation of yarn tension may be caused immediately downstream of thesensor.

The heat flux take up may be adjusted by adjusting the heat flux supplyin terms of temperature, pressure or fluid specific heat. The heat fluxmay be adjusted by use of a main and an auxiliary heater.

The heat flux take up may be adjusted by adjusting at least one of thetwist level and the speed of the yarn.

According to a particular aspect of the invention there is provided amethod of false twist texturing a yarn including:

providing a supply of yarn to be textured and take-up means for texturedyarn,

establishing a tensioned feed path for yarn to be textured between thesupply and the take-up,

providing in said feed path an input yarn drive, a yarn texturing stage,a textured yarn sensor giving a sensor output, an output yarn drive anda drive for the take-up means,

causing a relaxation of yarn tension at the sensor,

further providing yarn heater control means, and drive control means,

linking the textured yarn sensor in a control arrangement to at leastone of the yarn texturer and the yarn drives,

whereby yarn texture is maintained by response of the sensor to providesaid output to operate the control arrangement.

The yarn texturing stage may include a yarn heater, a yarn cooler and ayarn twister and twister drive.

The method may include providing the yarn heater in the form of a mainheater and an auxiliary heater, each with a respective control means,linking the textured yarn sensor output with the auxilliary heatercontrol means in said control arrangement, and causing or permitting thecontrol arrangement to adjust the auxilliary heater in response to thesensor output.

The method may include providing a heater having a high intensity heatflux. A jet or tube heater fed with hot fluid may be used as the highflux heater for yarn passed through it. The fluid may be heated bypassing it over a main heater and an auxiliary heater, each fluid heaterhaving control means incorporated in the control arrangement. The methodmay include controlling the flow of the heated fluid by the controlarrangement.

The method may include providing the textured yarn sensor as a yarnspeed sensor.

The relaxation of yarn tension may be caused immediately downstream ofthe sensor. The relaxation may be caused by a yarn tensioner immediatelydownstream of the sensor and before the output yarn drive. The methodmay include providing the textured yarn sensor as a yarn tension sensorbetween the intermediate yarn drive and the output yarn drive, with saidrelaxation adjacent the sensor.

The method may include providing the yarn twister and drive with a speedcontrol, linking the textured yarn sensor output with the yarn twisterdrive speed control in said control arrangement, and causing orpermitting the control arrangement to adjust the yarn twister speed inresponse to the sensor output.

The method may maintain a yarn texturing regime of yarn speed, yarntwister speed and yarn heater temperature, while varying at least one ofyarn twister speed and yarn heater temperature.

The method introduces texture into the heated yarn by sending yarn twistback up the feed path to the yarn in the heater. The texture is set byheating the yarn followed by cooling in the twisted state to below thesecond order transition temperature.

When one of the yarn twister drive speed and yarn heater are controlledin the control arrangement in response to the yarn sensor output theother may be kept constant.

Heat may be provided to the yarn heater and any auxiliary heater by anyconvenient hot fluid or a mixture of fluids. The hot fluid may besuperheated (dry) steam or hot compressed air. The texturing regime maybe maintained to a set drive speed, for example 2500 rpm ± 15 rpm.

The steam may be dried at 300° C.

The feed path is preferably substantially straight and may be in avertical or a horizontal line.

According to another aspect of the invention there is provided a methodof texturing yarn including

providing a supply of yarn to be textured and take-up means for texturedyarn,

establishing a feed path for yarn to be textured between the supply andthe take-up,

moving yarn from said supply into said feed path, drawing, heating andtwisting yarn in the feed path to form textured yarn, moving thetextured yarn along the feed path to the take-up means

causing the textured yarn to drive a yarn speed sensor,

causing or permitting a yarn relaxation immediately downstream of thesensor,

deriving from said sensor a control signal including a yarn speedcomponent,

applying the control signal to at least one of the driving of the yarn,the drawing of the yarn, the twisting of the yarn and the heating of theyarn,

whereby a selected yarn texture is maintained.

The method may achieve false-twist texturing of undrawn, partially drawnand drawn yarn.

The invention also provides apparatus to achieve control of yarn textureby feedback of the output of a direct-acting yarn texture sensor tocontrol at least one of yarn heater heat supply, yarn twist speed andyarn feed speed. The sensor may sense at least one of textured yarnspeed, yarn tension, yarn temperature and yarn bulk. The relaxation ofyarn desirably has unimpeded effect on the sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings in which

FIG. 1 shows an outline of a yarn texturing line embodying theinvention,

FIG. 1a shows a detail of part of FIG. 1,

FIG. 2 shows in more detail a yarn speed sensor, and

FIG. 3 shows in outline a control arrangement circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1 the yarn texturing line is straight from yarn supplyto yarn take-up. In other embodiments the line can be other thanstraight, for example folded through a right angle between the heatingand cooling stages, but the straight form has several advantages and asa texturing line embodying the invention need not be very long, and notas long as in the prior art, there is not the need to fold the line asin the prior art high speed machines.

In broad terms the line includes the following stages, a yarn supply(YC), a first yarn drive (FD), a yarn textured heater (TH) using steamin a heating jet, a cooler (TC) to set the textured yarn, a twistingdevice (TW), a second yarn drive (SD), a yarn speed sensor (YS), yarntensioner (YT) a third yarn drive (TD) and a yarn winder (YW). The lineis provided with steam supply (S1) for the texturing heater to produce ahigh and rapidly adjustable heat flux to the yarn. The line convenientlyincludes five separate drive means, e.g. electric motors with respectivespeed sensors (DS, FIG. 3) and respective controlled power supply andcontrol means (CPS, FIG. 3) for each yarn drive means. The five motorsare one for each of the three yarn drives, one for the yarn twister andone for the yarn winder. The yarn drives are conveniently a main drum onthe shaft of the motor with a small drum on a jockey arm urged againstthe main drum. Yarn may be taken once or twice round the small drum andanother pulley if required. A control arrangement, CN, shown in moredetail below, is provided for the whole line.

The yarn speed sensor YS is a very important element as accurate speedsensing is part of the control of the line and the sensor supplies ayarn speed signal for feedback to control at least one of yarn treatmenttemperature or the drives in a coordinated manner. The shaft speeds ofthe twister and the drive motors are measured by means of a slotted discmounted on the relevant shafts and fitted with photoelectric sensors.

FIG. 2 shows a form of yarn speed sensor found very suitable in anembodiment of the invention. The second yarn drive SD draws yarn fromthe twister TW and feeds it forward over a freely rotatable drum YSD inthe yarn speed sensor YS. The third yarn drive TD draws yarn from offthe drum YSD through a yarn tensioner YT and feeds the yarn forward tothe yarn winder YW. The drum YSD is freely rotatable at very high speed,corresponding to a yarn speed of some 2000 metres per minute or more, ona well-supported shaft which also carries a slotted disc DW forming partof a speed sensing arrangement for the drum. A photo-electric device WSis arranged to detect the rotation of the slotted disc to produce a drumspeed related pulse signal SI as sensor output. In operation to senseyarn speed yarn is wrapped only part-way round the drum and yarn tensioncontrolled to achieve very little slippage so that accurate speedsensing is provided. Conveniently about 30° wrap angle on the drum isused, the drum being about 40 millimetres in diameter. Greater amountsof wrap, including at least one full turn, may be used. The effect ofthe downstream tensioner device YT is needed to achieve suitable resultsfrom the speed sensor, however the effect may be produced by othermeans, for example, eddy current braking of the drum of the sensorthrough such action on the disc DW. The eddy current braking may bevariable by control action of the control system to vary the effect ofthe tension device. The nature of the effect is a slight reduction orrelaxation of yarn tension at the sensor compared with tension elsewherein the line, for example at drive C.

As so far described a very accurate yarn speed sensor YS has beenprovided. Similar slotted disc and photoelectric drive sensors aresuitable for drive sensors DS.

Returning again to FIG. 1 upstream from the sensor is the yarn texturingregion. Yarn from the supply YC is fed through a guide YG and atensioner FT to the yarn texturing heater TH by the action of the firstyarn drive FD drawing the yarn from the supply and feeding it to thetexturing heater in a controlled manner.

The texturing heater is supplied with steam which has come from a boilerover a superheating arrangement which has two heating sections, a first,main, superheater H1 and a second, auxiliary, heater H2. The firstheater receives dry steam (S1), which may already be superheated, andheats this as needed to produce steam at a controlled (SCl) basetemperature a little below that required to texture the yarn. Thesecond, auxiliary, heater receives the dry superheated steam from heaterH2 and is readily controllable (SC2) to heat the steam as needed so thatthe actual texturing temperature can be adjusted rapidly in a smallrange from the base temperature (set below the expected minimumtexturing temperature) upwards to beyond the expected maximum texturingtemperature. Advantageously the first heater H1 is controlled oradjusted so that the second heater H2 is at about 50% of power at thenominal setting of the texturing line. The main and supplemental heatersare conveniently electrically energised, as indicated by theconventional symbols. The second heater clearly must have a smallthermal mass to assist rapid response, also quick acting controls forthis heater are needed. Other hot fluids may be used, e.g. hotcompressed air or a mixture, such as air and steam.

In one embodiment the yarn texturing heater TH is similar to thestructure used in an earlier texturing process. The particular form ofheater is shown in general form in FIG. 1a but it is emphasised thatother forms of yarn texturising heater which achieve the heat flux fortakeup by the yarn may be used.

In the scrap-section of TH in FIG. 1 the flow of steam from the heatersH1 and H2 is identified at S2. The yarn enters the heater TH through anarrangement to resist escape of steam. The yarn passes through a chamberCH to which the steam supply S2 is admitted and the yarn and steam leavethe chamber CH, the yarn being textured (not shown) in the process andthe steam passing to any convenient exhaust or recovery ER.

In the yarn heater (TH) the yarn is heated by the heater, generally toabove the second transition temperature, by being brought into intimatecontact with a flow of heated fluid under pressure. From the yarn heaterthe yarn is supplied to a cooler TC of a water cooled trough throughwhich the yarn is drawn by yarn drive SD to ensure cooling below thesecond transition temperature. At the outlet of the cooler trough TC isa false twister TN driven at a controlled speed, which is convenientlyvariable.

The exact order and arrangement of the main and auxiliary heaters may bealtered while retaining the specified action, as will now be apparent tothose skilled in the art.

Various fluids may be mixed in a controlled manner to alter theeffective specific heat of the fluid providing the heat flux.

As now described yarn is supplied in a controlled manner to a closelycontrolled steam heater to be textured, and drawn through a cooler thena twister and moved onwards to be fed to an accurate yarn speedmeasuring stage to be then wound in any convenient manner but at acontrolled speed. The twister causes the twist to travel back along theyarn to the first drive FD, although in some cases fluid in the heatercan affect this twist travel, and even bring about pre-texturing. Thefirst drive sets the speed of the line.

A further important feature of the technique is that the auxiliaryheater can be controlled in dependence on measured yarn speed to achievea consistent required yarn quality, particularly important forconsistent dyeability.

The operating parameters of one embodiment of the invention areindicated by the following results of measurements on the equipment.(Yarn temperature was measured with a non-contact oscillating horizonpyrometer.):

    ______________________________________                                                        Yarn temperature                                                              (°C.)                                                  ______________________________________                                        I         Stem pressure                                                                 (psi)                                                                        90       200                                                                 100       199                                                                 120       202                                                                 140       204                                                         ______________________________________                                        II        Texturing steam                                                               temperature                                                                   (°C.)                                                                230       175.5                                                               240       183.5                                                               250       189.5                                                               260       196.5                                                               270       200                                                                 280       204                                                         ______________________________________                                    

The properties of the yarn produced are indicated by the followingmeasurements:

    ______________________________________                                        Material: POY polyester                                                       300f 30 to 167f 30                                                            ______________________________________                                        III (Temperature 220° C.)                                              Pressure        T        E          Bulk                                      (psi)           (CN/Tex) (%)        (K %)                                     ______________________________________                                         70             35.5     20.2       31.5                                       85             34.6     19.0       33.7                                      100             35.4     18.7       33.0                                      115             35.2     19.3       40.2                                      130             35.1     18.9       39.1                                      ______________________________________                                        IV (constant pressure)                                                        Temperature     T        E          Bulk                                      (°C.)    (CN/Tex) (%)        (K %)                                     ______________________________________                                        200             34.7     19.6       29.8                                      210             35.1     19.2       30.4                                      220             35.4     18.7       32.8                                      230             35.5     19.2       37.4                                      240             35.2     19.0       41.5                                      250             36.1     19.4       41.9                                      ______________________________________                                        V Dye uptake, Crimp centration                                                (10 readings at each point)                                                   Texturing Temperature                                                                       Dye uptake                                                                              Yarn contraction                                      Nominal (°C.) Variation                                                              (K/S)     % CV      (%)  % CV                                   ______________________________________                                        200   ±8.5 16.2      3.2       29.8 0.9                                    250   ±7.0 11.0      3.0       45.5 0.6                                    ______________________________________                                    

It will be noted from the above that in one embodiment of the inventionthe auxiliary heater is controlled in dependence on the measured yarnspeed and a control arrangement is provided to achieve this. In otherembodiments drive speed alone or drive speed and heating may beso-controlled to achieve an adequate control of yarn quality.

For a given yarn supply and texturing requirement a yarn speed isidentified for which steam or other hot fluid conditions are selected.The texturing line is then run and when a yarn speed change is sensedsteam conditions are altered to reverse the yarn speed change,maintaining the required texturing. This is on the basis that a primarycause of yarn speed change is believed to be a change of texturing whichaffects the relaxation of the yarn at the yarn speed sensor. Thetemperature of the yarn exiting from the heater is also usable as thebasis of the control of texturing.

FIG. 3 shows in outline a control arrangement of a feedback loopincluding a small computer PC to carry out the appropriate calculationsfrom the information (SI) supplied from the yarn speed sensor (YS) andthe respective drive speed sensors (DS) to provide control informationto the respective inverters driving each drive motor with drive powerDP. Those skilled in the art will be aware of the conventionaltechniques available to provide such an arrangement.

Preferably the speeds of drives FD, SD and TD are established in aparticular relationship (not always equal speeds) for a required yarntexturing action and kept in this relationship while texturing isadjusted to the required action by control of heating and/or twist and/or speed.

Two examples of the control of yarn texturing in accordance with theinvention are as follows, the yarn being 167 dtex (34 fils) polyesteryarn with steam at 100 psi pressure and approximately 200° C. (thespeeds are rounded values):

    ______________________________________                                        Nominal yarn throughput speed                                                                            600     800                                        (m/min)                                                                       Feed roller        FD      556     769                                        (m/min)                                                                       False twist motor  TW      7136    9514                                       (rpm)                                                                         First output roller                                                                              SD      600     800                                        (m/min)                                                                       Second output roller                                                                             TD      598     798                                        (m/min)                                                                       Take-up drive      YW      569     757                                        (m/min)                                                                       ______________________________________                                    

In one arrangement the steam heater has a main heater with a rating ofsome 2.5 KW and an auxiliary heater with a rating of some 800 W. Eachheater has a semiconductor power controller. For the main heater thesetting can be controlled in accordance with a look-up table for yarntype and texturing and will typically be at about 1 KW. The auxiliaryheater is controlled continuously at a rate of a few cycles/second to afew tens of cycles/second. Typically the auxiliary power level is about400 W. The power supply is conveniently at mains potential, say 110 or240 volts ac. If heated air is used the temperature will be some 200° C.to 220° C., depending on the yarn.

As described above the yarn sensor is a yarn speed sensor but a yarntension sensor giving an appropriate output is also suitable. The changein textured yarn speed speed or tension when the drive conditions fordrives FD, SD and TD are accurately maintained constant indicates thatyarn texturing has deviated from a desired set condition. Other sensorsare possible as the source of control information for the closed loopcontrol of heat flux taken up by the yarn, for example yarn bulk or yarntemperature at the heater exit.

Earlier attempts to make the machines smaller of necessity means the useof small heaters, which in turn means that the heaters have to be of ahigh intensity. The high intensity means that either they have to be sohot that they melt the yarn if there is a yarn breakage, or they have tobe of tubular or jet design with narrow orifices using hot fluid underpressure. The narrow orifices quickly change in dimension with time, dueto the deposition of spin finish and oligomer and so the heat transfercharacteristics of the heater change. The above techniques correct forthese and other changes in heating characteristics so as to permit theuse of small high intensity heaters which transfer a constant amount ofheat (heat flux) to the yarn (albeit by altering the temperature of thefluid in the jet as the flow rate of the fluid changes due to changes inthe sizes of the orifices), which in turn permits the use of shortthreadlines which in turn, due to the reduction in surging, permits theuse of much higher speeds than current large machines. This alsoachieves the important result of consistent dyeability. While smallerheaters are made possible by the invention the techniques of theinvention need not be restricted to such heaters. The use of controlledheaters in closed loops provides for non-isothermal operation of amultiple position machine when modified as will be apparent to thoseskilled in the art in view of above disclosed techniques.

The technique is described for a horizontally arranged feed path but avertical path is also possible and will be much more compact andeconomical than the current technology using extended heaters andcoolers. The accurate sensing of the textured yarn condition such asspeed or tension permits the degree of texturing to be assessedcontinuously and continuous on-line maintenance of required texturing tobe achieved by control of yarn drive speeds and/or texturing conditions.In particular consistency of dyeability of textured yarn produced from aspecific supply of yarn can be achieved even when the yarn is texturedin several positions in a machine.

I claim:
 1. A method of manufacturing a textured yarn comprising thesteps of:feeding a yarn to be textured from a supply thereof to atake-up means for the textured yarn along a path including a texturingzone; false twisting the yarn so that it is twisted in the texturingzone; heating then cooling the twisted yarn in the texturing zone toproduce a false twist textured yarn; sensing a condition of the yarn ata position in said path; providing adjustability of at least one of saidfeeding, false twisting and heating and cooling steps; and adjusting atleast one of said steps for which adjustability is provided inaccordance with the condition sensed in said sensing step, wherein thecondition sensed in said sensing step comprises yarn speed while tensionin the textured yarn is relaxed at a position in said path between thetexturing zone and the take-up means.
 2. A method according to claim 1,wherein tension in the yarn is relaxed by overfeeding the yarn.
 3. Amethod according to claim 2, wherein the tension-relaxed yarn runs overa freely-rotatable drum, wherein a speed of the yarn is sensedphotoelectrically.
 4. A method according to claim 1, wherein the heatingstep being effected by a hot fluid.
 5. A method according to claim 4,wherein the hot fluid comprises steam.
 6. A method according to claim 4,wherein the hot fluid comprises hot air.
 7. A method according to claim4, wherein the temperature of the hot fluid is adjusted in accordancewith the condition sensed.
 8. A method according to claim 7, wherein thetemperature of the hot fluid is adjusted by a rapid response heater. 9.A method according to claims 7, wherein the temperature of the hot fluidis adjusted by a main heater and a supplemental rapid response heater.10. A method according to claim 1, wherein said feeding step iscontrolled by feeding the yarn by speed-controllable feed rollers,wherein a speed of at least one feed roller is controlled in accordancewith the condition sensed in said sensing step.
 11. A method accordingto claim 1, wherein said false twisting step is controlled by falsetwisting the yarn with a rotating false twist device and the speed ofthe false twist device is adjusted in accordance with the conditionsensed in said sensing step.
 12. A method according to claim 1,comprising adjusting at least one of said steps for which adjustment isprovided by a closed loop feedback control arrangement in order tomaintain the condition sensed constant.
 13. A method for texturizing ayarn comprising:feeding the yarn under tension-from a source to atake-up therefor along a path, said path including a false twist zone;heating and cooling the yarn in said false twist zone while the yarn ishighly twisted thereby texturizing the yarn; and controlling aprocessing parameter effecting the texture of yarn in the false twistzone, said processing parameter being controlled in accordance with theresult of a measurement made on the yarn travelling along said pathafter leaving the false twist zone, said measurement being indicative ofthe effect of the texturizing on the yarn, wherein the measurement isindicative of the dyeability of the texturized yarn.
 14. A methodaccording to claim 13, in which measurement is made on the yarn intension-relaxed conditions between the false twist zone and the take-up.15. A method according to claim 13, in which the yarn drives in rotationa freely-rotatable drum, wherein a speed of the yarn is sensed as themeasurement.
 16. A method according to claim 15, in which the speed issensed photoelectrically.
 17. A method according to claim 13, in whichmeasurement is made on the yarn in the false twist zone.
 18. A methodaccording to claim 17, in which yarn temperature on leaving a yarnheater is measured as an indication of heat take-up by the yarn.
 19. Amethod according to claim 13, in which the measurement is used tocontrol the processing parameter in a closed-loop control system.
 20. Amethod according to claim 13, in which the measurement is used tocontrol yarn heating.
 21. A method according to claim 20, in which yarnheating is effected by direct heat exchange with a hot fluid, whereinthe fluid temperature is controlled in accordance with the measurement.22. A method according to claims 21, in which the fluid is heated inmain and auxiliary heaters of which the auxiliary heater is controlled.23. A method according to claim 13, in which the measurement is used tocontrol yarn tension in the false twist zone.
 24. A method according toclaim 23, in which yarn tension is controlled by controlling the speedof at least one yarn feed roller.
 25. A method according to claim 13, inwhich the measurement is used to control yarn twist level in the falsetwist zone.
 26. A method according to claim 25, in which the twist levelis controlled by controlling the speed of rotation of a rotary falsetwist device.
 27. A method for texturizing a yarn comprising:feeding theyarn under tension from a source to a take-up therefor alone a path,said path including a false twist zone; heating and cooling the yarn insaid false twist zone while the yarn is highly twisted therebytexurizing the yarn; and controlling a processing parameter effectingthe texture of the yarn in the false twist zone, said processingparameter being controlled in accordance with the result of ameasurement made on the yarn travelling along said path after leavingthe false twist zone, said measurement being indicative of the effect ofthe texturizing on the yarn, wherein the measurement is indicative ofthe bulk of the texturized yarn.
 28. A method according to claim 27, inwhich the measurement is used to control yarn heating.
 29. A methodaccording to claim 28, in which yarn heating is effected by direct heatexchange with a hot fluid, wherein the fluid temperature is controlledin accordance with the measurement.
 30. A method according to claim 29,in which the fluid is heated in main and auxiliary heaters of which theauxiliary heater is controlled.
 31. A method according to claim 27, inwhich the measurement is used to control yarn tension in the false twistzone.